Composite materials offer potential design improvements in gas turbine engines. For example, in recent years composite materials have been replacing metals in gas turbine engine fan blades because of their high strength and low weight. Most metal fan blades for a gas turbine engine are titanium. The ductility of titanium fan blades enables the fan to ingest a bird and remain operable or be safely shut down. The same requirements are present for composite fan blades.
A composite fan blade can have a sandwich construction with a three-dimensional woven core at the center and two-dimensional filament reinforced plies or laminations on either side. To form the composite blade, individual two-dimensional laminations are cut and stacked in a mold with the woven core. The woven core extends from the root to the tip of the blade and the plies are stacked on either side of the woven core to form the desired exterior surface profile. The mold is injected with a resin using a resin transfer molding process and is cured. A composite fan blade can also be made only of the two-dimensional laminate plies without the woven core.
A composite blade has a root, which connects to the fan mechanism, and a tip opposite the root. A composite blade for a turbine engine fan blade is typically designed with a divergent root portion known as a dovetail root. The thickness of the blade greatly changes over a short length at the dovetail root. The dovetail root enables the airfoil to withstand typical operational loads from rotation and bending and loads from foreign object strikes. The dovetail root typically slides into a slot in a disc or a rotor to hold the airfoil in place while the disc or rotor is spinning.